Hi, I’ve heard about animals which haven’t changed a lot since a loooong time ago (tuataras, aardvarks, coelacanths and nautiluses are some examples). But I have also heard, that all animals’ genes change over time, even when they remain in the same ecological niche. If that is true, no animals can be exactly - or even nearly - identical to their prehistoric ancestors. What is true? Or are the animals called “living fossils” just the only living descendants of the prehistoric animals? Are “living fossils” called living fossils because they have maintained the prehistoric animals’ physical/behavioral characteristics, making “living fossil” a non-genetic term?
Your last guess is correct. There are species that have remained morphologically identical, or nearly identical, for millions and millions of years. But for the most part we don’t know the genetics of the early ancestors, we don’t have DNA samples for them, only fossils.
This. And, in fact, generally only the physical bit, it’s really hard to peg behaviour from most fossils. But yes, everything alive today is just as evolved as everything else, so while that nautilus or coelacanth may look like something from 100M years ago, you can better your bottom dollar it’s not the same, genetically.